Electrical service providers such as electrical utilities employ electricity meters to monitor energy consumption by customers (or other entities). Electricity meters track the amount of energy consumed by a load (e.g. the customer), typically measured in kilowatt-hours (“kwh”) at each customer's facility. The service provider uses the consumption information primarily for billing, but also for resource allocation forecasting and other purposes.
One problem with many electricity meters is that external forces can sometimes alter the accuracy of the metering operation. While meters are typically housed in a manner that reduces the impact of external elements, there are some circumstances in which external forces become an issue. For example, it is known that current sensors currently used in many electricity meters have sensitivity to strong magnetic fields. Strong magnetic fields can affect the ability of certain current sensors to measure the current provided to the load. Without accurate current measurements, the energy consumption measurement will exhibit errors.
The problems arising from the exposure of an electricity meter to strong externally generated magnetic fields is discussed, by way of example, in U.S. Pat. No. 7,495,555, which is incorporated herein by reference.
To combat potential magnetic field issues, it has been known to place a ferromagnetic shielding structure around the CT or the entire interior of the meter to reduce the impact of the magnetic field on interior components. However, magnetic shielding requires additional material and labor cost, and undesirably increases the weight of the meter.
It is also known to employ a sensor to detect and flag excess magnetic fields within the meter. See U.S. Patent Publication No. 2010/0072990 and U.S. Pat. No. 7,495,555 for examples of this method. A drawback to the sensor method is the requirement for additional equipment in the meter (in the form of the magnetic sensors). In addition, retrofitting existing meters in the field with such capabilities is not plausible because it requires installation of new circuitry within the meter.
There is a need, therefore, for a more cost-effective approach to combating the potential for inaccurate metering due to excess magnetic fields that has reduced equipment cost. There is also a need for an approach to combating issues relating to excessive magnetic fields that can be more readily retrofitted into existing meters.